Forecasting Sunspots

Movie of the detected travel-time perturbations before the emergence of active region
10488. First 10 seconds show intensity observations. The intensity later fades out and the
photospheric magnetic field is shown. Next 20 seconds, zoom in to a region where a
sunspot group would emerge. The upper layer shows magnetic field observations at the surface
and the lower layer shows simultaneous travel-time perturbations, detected at a depth of
about 60,000 km. After the emergence, intensity observations show the development of this
active region, until it rotates out of the field of view. (Movie made by T. Hartlep)

Movie shows the detected travel-time perturbations during the emergence of active region
11158. First 12 seconds of the movie show photospheric intensity observations (orange
color) of the region, and travel-time perturbations detected at a depth of about 60,000 km
(blue-red color). Then, movie shows sunspots (blue and orange) on the solar surface and
coronal loops (light green) observed by SDO/AIA. (Movie made by T. Hartlep and S.
Winegarden)

Images of surface and subsurface magnetic activity of active region 10488. The
upper layer
shows the photospheric magnetic field, and the lower layer shows the acoustic travel-time
perturbations detected at a depth of about 60,000 km. The left image was taken at about
03:30 UT 26 October 2003 and the right image about 2 days later.

Acoustic travel-time perturbations detected at a depth of about 60,000 km (left)
and
simultaneous observations of the photospheric intensity (middle) and magnetic field (right).
The images of the upper row were taken at about 03:30 UT 26 October 2003 and those of the
lower row about 2 days later.

Stanford University scientists, analyzing archival data from the Michelson Doppler Imager
(MDI) on SOHO, have for the first time succeeded in detecting sunspot regions in the deep interior of
the Sun, 1-2 days
before they appear at the solar surface.

Sunspots, dark features in the solar photosphere with strong magnetic fields, have been
observed for more than 400 years. They are the most visible components of regions where
solar flares and coronal mass ejections (CMEs) occur, which may cause power outages and
interruptions of telecommunication and navigation services on the Earth. Although it is
widely believed that sunspot regions are generated in the deep solar interior, the emergence
of these regions through the convection zone to the photosphere has remained undetected
until now.

The results of the Stanford scientists show that sunspots are generated at least 60,000 km
below the surface and emerge from this depth up to the surface with an average speed of
0.3-0.6 km/s. The detection of sunspots in the solar interior may lead to significant
advances in space weather forecasting. The technique that they used to detect the sunspots
is called "time-distance helioseismology", which is similar to an approach widely used in
earthquake studies. Just as seismic waves traveling through the body of Earth reveal what is
inside the planet, acoustic waves traveling through the body of the Sun can reveal what is
inside the star. Submerged sunspots have a detectable effect on the sun's inner
acoustics—namely, sound waves travel faster through a sunspot than through the surrounding
plasma. A big sunspot can leapfrog an acoustic wave by 12 to 16 seconds.

The results are reported in the paper "Detection of Emerging Sunspot Regions in the Solar
Interior" by Stathis Ilonidis, Junwei Zhao, and Alexander Kosovichev, published in the
August 19 issue of Science (Vol. 333, pp. 993-996, 2011).